Europace Advance Access originally published online on May 10, 2006
Europace 2006 8(6):421-422; doi:10.1093/europace/eul046
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AVNRT
Spontaneous high degree atrioventricular block during AV nodal re-entrant tachycardia
Department of Pacemaker and Electrophysiology, Rajaie Cardiovascular Medical and Research Center, Iran University of Medical Sciences, M, ellat Park, Vali-e-Asr Avenue, P.O. Box 15745-1341, Tehran 1996911151, Iran
Manuscript submitted 3 October 2005. Accepted after revision 12 March 2006.
* Corresponding author. Tel: +98 21 2202 8313; fax: +98 21 2204 8174. E-mail address: bkazemia1966{at}gmail.com
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Abstract |
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High-degree atrioventricular (AV) block during AV nodal re-entrant tachycardia (AVNRT) is considered a rare phenomenon. A patient with slow–fast AVNRT and transient high-degree AV block is presented. Electrophysiological manoeuvres identified the site of block in the lower common pathway of the AV node. This arrhythmia was rendered non-inducible after slow pathway ablation.
Key Words: Atrioventricular nodal re-entry, Atrioventricular block, Lower common pathway
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Case report |
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A 44-year-old woman underwent electrophysiological study for frequent episodes of supraventricular tachycardia. She had no structural heart disease and baseline 12-lead ECG was normal. The surface ECG during the arrhythmia showed a regular narrow QRS tachycardia. During electrophysiological study, AH and HV intervals were 50 and 40 ms, respectively. At baseline, typical AV nodal re-entrant tachycardia (AVNRT) was reproducibly induced during atrial stimulation following an AH interval gap. The arrhythmia was characterized by a cycle length of 250 ms, AH 196 ms, and HA 60 ms. During one of the episodes (Figure 1), sudden high grade AV block occurred, long after induction and continued as 2:1 AV block before converting spontaneously to 1:1 AV conduction. HV intervals after tachycardia onset and immediately before the occurrence of AV block were the same (45 ms). Transient RV apical pacing during tachycardia at a cycle length shorter than that of the tachycardia (220 ms) entrained the atrium with 1:1 VA conduction and showed a V-A-V response on termination of pacing (Figure 2). Following successful slow pathway ablation, no tachycardia was inducible. During 7 months of follow-up, she has remained free of symptoms without receiving any anti-arrhythmic drugs.
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This case shows a supraventricular tachycardia with a relatively long episode of high degree AV block. Possible diagnoses included typical AVNRT and atrial tachycardia (AT) with long PR interval. Although AT with long PR could be proposed as a diagnostic possibility, it is excluded by the presence of V-A-V pattern immediately after termination of overdrive ventricular pacing and the very short HA interval.1
During AV block, His potentials were not seen in non-conducted beats despite arrhythmia continuation. This may suggest that the site of block was above the His level (i.e. intranodal), although infra-Hisian block could not be ruled out.2 This makes a strong argument in favour of a block in the lower common pathway in AVNRT, as demonstrated by the presence of retrograde atrioventricular block during ventricular pacing at the same cycle length as AVNRT. Presence of lower common pathway and 2:1 AV block during arrhythmia have been documented by ventricular pacing protocols in about 20 and 10% of patients with AVNRT, respectively.2 However, AV block is more often induced in the electrophysiological laboratory, than seen clinically.2 It is generally believed that the cause of block is functional. There is controversy about the exact site of the functional block. Man et al.2 have proposed an intra-Hisian site, irrespective of the presence or absence of His potential during AV block because atropine had no effect on 2:1 AV block during AVNRT.
Our study was limited by the fact that we did not assess the effects of physiological (e.g. Valsalva manoeuvre or deep inspiration) or pharmacological (e.g. adenosine or atropine) interventions during the arrhythmia. Although these manoeuvres could provide further insight into the mechanism of the arrhythmia or the site of block, the data obtained seem sufficient to arrive at the correct diagnosis.
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[1] –Knight BP, Ebinger M, Oral H, et al. Diagnostic value of tachycardia features and pacing maneuvers during paroxysmal supraventricular tachycardia. J Am Coll Cardiol 2000; 36: 574–82.
[2] –Man KC, Brinkman K, Bogun F, et al. 2:1 atrioventricular block during atrioventricular nodal reentrant tachycardia. J Am Coll Cardiol 1996; 28: 1770–4.[Abstract]
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